It applies in particular to bridge cable-stayed suspensions. The stays vibrate in particular because of the wind and the vehicle traffic. Various types of device have been proposed for damping these vibrations.
In a first type of damping device (see for example EP 0 343 054 A1, DE 295 17 250 U1 or WO 98/04780 A1), the vibratory energy is dissipated around the cable, in a zone delimited radially by an element fixed to the suspended structure. This element may be an arm extending between the cable and the suspended structure, or a tube receiving the bottom part of the cable. The amplitudes of the damped vibrations are limited with this type of device.
Other devices use linear-stroke dampers such as hydraulic pistons. These pistons may be disposed on arms extending between the cables and the suspending structure (see for example JP 09-59921 A) or between the cable and a tube fixed to the suspended structure and containing the bottom part of the cable (see for example FR 2 859 260 A1 or JP 06-58370 A).
A so-called pendular damping device comprises an oscillating arm connected to the cable, the oscillations of which are damped by viscous friction. FR 2 664 920 A1 describes an example of such a pendular device.
In an embodiment of the pendular damping device as depicted in FIG. 1, the arm 10 oscillates about a pivot 11 installed on a support 12 itself pivoting on a chassis 13 fixed to the bridge deck 14. Two hydraulic pistons 15 disposed in an X are mounted between the bottom part of the arm 10 and the chassis 13 or the deck 14. The vertical movements of the stay 16, held in a coupler 17 at the top part of the arm 10, are damped by the pistons 15 when the arm 10 moves up and down, the vertical movements of the pivot 11 being accepted by inclination of the support 12. The horizontal movements of the stay 16 make the arm 10 oscillate about the pivot 11 and are damped differentially by the crossed pistons 15.
The pendular device provides strong damping on the cables, in particular long cables. It is typically situated at the bottom part of the cable, at approximately 2%-3% of its total length from the bottom anchorage. The design of this device makes it possible to damp both the vertical and transverse movements of the cable, over long strokes, around typically ±100 mm to approximately ±150 mm.
However, the deviations of the cables are sometimes even greater, in particular when the structure is flexible. The necessary strokes are even greater, and may for example range up to ±700 mm.
The concept of the pendular device then therefore has its limits since the pistons have very long strokes, the device becomes excessively bulky, as shown by FIG. 1. A damping piston typically has a length of three times its stroke, so that there may be a need for pistons more than 2 metres long. It becomes almost impossible to position such a bulky pendular device on a bridge.
An object of the present invention is to improve the pendular device and to facilitate insertion thereof in the structure, in particular if the amplitudes of the vibrations to be damped are large.